1. Field of the Invention
The present invention relates to a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, and more particularly to a bandwidth allocation system of a virtual path capable of dynamically controlling a bandwidth allocation ratio depending on a bandwidth ratio adopted in the virtual paths.
2. Description of the Related Art
In an asynchronous transfer mode exchange for use in multi-media communication (hereinafter, referred to as ATM), a virtual path is established between ATM nodes, so to connect a virtual channel. A bandwidth of a virtual path which would be established depending on input traffic is usually fixed, in a large key network. However, when one ATM node accommodates only some hundreds of subscribers like a subscriber access line, a bandwidth used for a virtual path varies extremely, and therefore a bandwidth established for a virtual path would become greater, as contrasted with an average bandwidth generally used. Then, it is necessary to multiplex a plurality of virtual paths, so to make them effectively group, thereby absorbing fluctuation of a bandwidth of each virtual path so as to reduce the whole required bandwidths, in an ATM relay node for exchanging a plurality of virtual paths to transfer data to a physical medium.
In this case, since a bandwidth established for each virtual path is not assured completely, it is necessary to allocate a bandwidth dynamically depending on the necessity. This conventional technique for dynamic bandwidth allocation is disclosed in, for example, Japanese Patent Publication Laid-Open (Kokai) No. Heisei 6-209329, xe2x80x9cBandwidth Allocation Method for Virtual Path in Asynchronous Transfer Modexe2x80x9d.
The structure of an AMT node for realizing the conventional dynamic bandwidth allocation method disclosed in the same publication will be described with reference to FIG. 8. As illustrated in FIG. 8, the ATM node 800 comprises a bandwidth monitor circuit 8000, a detecting circuit of excess of the upper threshold of Queue length 8010, a waiting time prediction circuit 8020, a bandwidth ratio allocation control circuit 8030, an output bandwidth control circuit 8040, and cell stored buffers 8050-1 to 8050-4 respectively established for virtual paths 8200-1 to 8200-4.
Cells to be transferred through the virtual paths 8200-1 to 8200-4 are supplied to the bandwidth monitor circuit 8000 via physical mediums 8060-1 to 8060-4. The bandwidth monitor circuit 8000 monitors input cells, calculates a bandwidth adopted to every virtual path 8200-1 to 8200-4, and transfers the cells to the corresponding cell stored buffers 8050-1 to 8050-4 respectively. The cell stored buffers 8050-1 to 8050-4 respectively holding the upper thresholds TH-1 to TH-4 of the Queue length store the input cells and supply the input cells to a physical medium 8070 according to the output bandwidths established by the output bandwidth control circuit 8040.
The Queue length of a cell stored buffer 8050-i (i=1, 2, 3, 4) is always monitored by the Queue length upper threshold excess detecting circuit 8010. When the Queue length becomes equal to the upper threshold TH-i, the Queue length upper threshold excess detecting circuit 8010 sends a control signal 8100 to the bandwidth ratio allocation control circuit 8030. This processing by the Queue length upper threshold detecting circuit 8010 enables detection of congestion in a cell stored buffer. In the conventional technique disclosed in the same publication, the waiting time prediction circuit 8020 is adopted to detect the congestion of a cell stored buffer by calculating the waiting time of each cell within the cell stored buffers 8050-1 to 8050-4, in order to detect the congestion in a cell stored buffer assuredly. The waiting time prediction circuit 8020 calculates the waiting time of each cell within the cell stored buffers 8050-1 to 8050-4, according to the bandwidth used for each virtual path 8200-1 to 8200-4 obtained by reference to the bandwidth monitor circuit 8000 and the output bandwidth of each cell stored buffer 8050-1 to 8050-4 obtained by reference to the output bandwidth control circuit 8040. When the calculated waiting time exceeds a predetermined allowance, a control signal 8110 is sent to the bandwidth ratio allocation control circuit 8030. The bandwidth ratio allocation control circuit 8030, upon receipt of the both control signals 8100 and 8110, refers to the current bandwidth information of the virtual paths 8200-1 to 8200-4 from the bandwidth monitor circuit 8000, regards the current bandwidth ratio as the bandwidth allocation ratio, and notifies the output bandwidth control circuit 8040 of the bandwidth allocation ratio by use of a control signal 8120. While, the output bandwidth control circuit 8040, upon receipt of the control signal 8120, calculates each output bandwidth of the cell stored buffers 8050-1 to 8050-4 according to the received bandwidth allocation ratio and modifies the output bandwidth depending on the necessity. A cell stored buffer 8050-1, 2, 3, or 4 having the modified output bandwidth supplies the cell within the same buffer to the physical medium 8070 in accordance pith the modified output bandwidth.
The above-mentioned conventional ATM node is defective in requiring too much processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold.
More specifically, in allocating an output bandwidth of each cell stored buffer when the Queue length of a cell stored buffer becomes equal to the upper threshold, the conventional ATM node regards the transmission bandwidth of a physical medium on the output side as a bandwidth to be allocated and allocates this bandwidth as the output bandwidth of each cell stored buffer according to a current bandwidth ratio of each virtual path entered into each cell stored buffer. In this case, since the output bandwidth of a cell stored buffer is allocated equally to the bandwidth used for a virtual path entered into the cell stored buffer, the Queue length remains around the upper threshold thereof. Therefore, fluctuation of the bandwidth used for a virtual path entered into a cell stored buffer may increase the opportunity of the Queue length becoming equal to the upper threshold, resulting in an increase of the processing amount of bandwidth allocation control.
A first object of the present invention is to provide a bandwidth allocation system of a virtual path in a communication network of asynchronous transfer mode, which is able to reduce the processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold thereof.
A second object of the present invention is to provide a bandwidth allocation system of a virtual path in a communication network of asynchronous transfer mode capable of making effective use of bandwidth among cell stored buffers, as well as reducing the processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold thereof.
According to the first aspect of the invention, a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, wherein
a node in the asynchronous transfer mode network comprises
bandwidth monitor means for calculating a bandwidth used for a virtual path by measuring a cell amount entered into each virtual path,
cell storing means for storing the input cell for every virtual path,
bandwidth allocation control means for deciding a bandwidth allocation ratio for output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means depending on a change of the Queue length in the cell within the cell storing means, and
output bandwidth control means for controlling output of the respective cell storing means, in accordance with the bandwidth allocation ratio decided by the bandwidth allocation control means.
In the preferred construction, the bandwidth allocation control means allocates an output bandwidth much more than a used bandwidth with respect to the cell storing means in which the increasing Queue length of the cell exceeds a predetermined value.
In another preferred construction, an upper threshold of cell storing amount in the cell storing means is established, and
the bandwidth allocation control means,
referring to a bandwidth used for each virtual path from the bandwidth monitor means, decides a bandwidth allocation ratio of output bandwidths with weight added thereto according to the used bandwidth ratio, when the Queue length of a cell within the cell storing means exceeds the upper threshold.
In another preferred construction, an upper threshold of cell storing amount in the cell storing means is established, and
the bandwidth allocation control means
includes Queue length upper threshold excess detecting means, monitoring the Queue length of a cell within the cell storing means, for supplying a detection signal when the increasing Queue length exceeds the upper threshold, and
decides a bandwidth allocation ratio of output bandwidths with weight added thereto according to a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, in reply to the detection signal from the Queue length upper threshold excess detecting means.
In another preferred construction, the bandwidth allocation control means
allocates an output bandwidth much more than a used bandwidth with respect to the cell storing means in which the increasing Queue length exceeds a predetermined value, and
after providing the above-mentioned cell storing means with a much more output bandwidth, surplus bandwidth allocation to the cell storing means is released when the Queue length of the cell in the cell storing means is reduced to a predetermined value.
According to the second aspect of the invention, a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, wherein
a node in the asynchronous transfer mode network comprises
bandwidth monitor means for calculating a bandwidth used for a virtual path by measuring a cell amount entered into each virtual path,
cell storing means for storing the input cell for every virtual path,
bandwidth allocation control means for deciding a bandwidth allocation ratio for output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means depending on a change of the Queue length in the cell within the cell storing means, and
output bandwidth control means for controlling output of the respective cell storing means, in accordance with the bandwidth allocation ratio decided by the bandwidth allocation control means,
an upper threshold and a lower threshold of a cell storing amount in the cell storing means are established, and
the bandwidth allocation control means includes
bandwidth weight allocation control means for deciding a bandwidth allocation ratio of output bandwidths, with weight added thereto according to a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, when the Queue length of a cell within the cell storing means exceeds the upper threshold, and
bandwidth ratio allocation control means, after decision of the bandwidth allocation ratio by the bandwidth weight allocation control means and output control of the respective cell storing means by the output bandwidth control means, for deciding a bandwidth allocation ratio of output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, when the Queue length arrives at the lower threshold.
In the preferred construction, the bandwidth allocation control means includes
Queue length upper threshold excess detecting means, monitoring the Queue length of a cell within the cell storing means, for supplying a detection signal when the increasing Queue length exceeds the upper threshold,
bandwidth weight allocation control means for deciding a bandwidth allocation ratio of output bandwidths, with weight added thereto according to a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, in reply to the detection signal from the Queue length upper threshold excess detecting means,
Queue length lower threshold arrival detecting means, monitoring the Queue length of a cell within the cell storing means, for supplying a detection signal when the Queue length is reduced to the lower threshold, after decision of the bandwidth allocation ratio by the bandwidth weight allocation control means and output control of the respective cell storing means by the output bandwidth control means, and
bandwidth ratio allocation control means for deciding a bandwidth allocation ratio of output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, in reply to the detection signal from the Queue length lower threshold arrival detecting means.
In another preferred construction, the bandwidth allocation control means includes
Queue length upper threshold excess detecting means, monitoring the Queue length of a cell within the cell storing means, for supplying a detection signal when the increasing Queue length exceeds the upper threshold,
bandwidth weight allocation control means for deciding a bandwidth allocation ratio of output bandwidths, with weight added thereto according to a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, in reply to the detection signal from the Queue length upper threshold excess detecting means,
Queue length lower threshold arrival detecting means, monitoring the Queue length of a cell within the cell storing means, for supplying a detection signal when the Queue length is reduced to the lower threshold, after decision of the bandwidth allocation ratio by the bandwidth weight allocation control means and output control of the respective cell storing means by the output bandwidth control means,
bandwidth ratio allocation control means for deciding a bandwidth allocation ratio of output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor means, in reply to the detection signal from the Queue length lower threshold arrival detecting means, and further includes
state control means for controlling state of the Queue length of a cell within the cell storing means;
the state of the cell storing means controlled by the state control means is changed according to the detection results of the Queue length upper threshold excess detecting means and the Queue length lower threshold arrival detecting means; and
the bandwidth weight allocation control means and the bandwidth ratio allocation control means judge whether decision processing of a bandwidth allocation ratio should be performed or not, with reference to the state of the cell storing means controlled by the state control means.
In another preferred construction, the state control means stores identification information for identifying the cell storing means, information indicating whether the Queue length is reduced to the lower threshold or not after once getting equal to the upper threshold, in every identification information, and information indicating an output bandwidth.
According to another aspect of the invention, a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, wherein
a node in the asynchronous transfer mode network comprises
a bandwidth monitor for calculating a bandwidth used for a virtual path by measuring a cell amount entered into each virtual path,
a cell stored buffer for storing an input cell for every virtual path,
a bandwidth allocation control circuit for deciding a bandwidth allocation ratio for output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidth used for every virtual path from the bandwidth monitor depending on a change of the Queue length in the cell within the cell stored buffer, and
an output bandwidth control circuit for controlling output of the respective cell stored buffers, in accordance with the bandwidth allocation ratio decided by the bandwidth allocation control circuit.
Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow.